The invention relates to a method for detecting an open line of the sinusoidal coil or the cosinusoidal coil of a resolver and a circuit for implementing this method.
Resolvers are used for determining the angular position of a rotating object, e.g. the driveshaft of an engine. In the prior art, there are various types of resolvers. In principle, a varying magnetic field is here generated by means of a coil and this field is detected by means of at least one further coil, the strength of the coupling between the coils varying in dependence on the position or angular position to be measured. In the case of the “variable reluctance resolver” (VR resolver), for example, only one exciter coil is used and there are two measuring coils which generate position-dependent signals. German patent application DE 10 2011 078 583 A1, for example, discloses an evaluation of resolver sensor signals in a vehicle. For this purpose, a resolver picks up a rotating movement of a rotor and a processor element processes the sinusoidal and cosinusoidal output signals of the resolver.
The invention is based on such a resolver, the exciter signal being sinusoidal and typically having a frequency of 10 kHz. The two measuring coils are, as a rule, positioned orthogonally with respect to one another and are designated as sinusoidal and cosinusoidal coil. By means of the two measurement signals, the angle of the object being measured can be unambiguously determined.
For example, the exciter signal for the exciter coil can be provided by two push-pull output stages, one each for the two terminals of the exciter coil. The output signals of the two output stages are then phase-shifted by 180° to one another and the exciter signal effective for the exciter coil is the differential voltage between the outputs of the two output stages.
However, there is also a possibility of operating the exciter coil by only one output stage. The second terminal of the exciter coil is then applied either directly or via a capacitor to a fixed potential, e.g. ground potential.
At the receiver coils, an alternating-voltage signal having the same frequency as the exciter signal is then produced, the amplitude of which, however, is modulated in accordance with the position of the rotor, the signal at the cosinusoidal coil being phase-shifted by 90° with respect to the signal at the sinusoidal coil.
Resolvers are frequently used for controlling permanently excited synchronism machines (PSM) and electrically excited synchronism machines (ESM) which, e.g., are used as drive for hybrid and electric vehicles. Such a control requires the knowledge of the current angle position of the rotor. The control of asynchronous machines (ASM) requires the knowledge of the current frequency of the drive.
Because of their ruggedness, resolvers are preferably used for these purposes in motor vehicles even if there are alternative sensors, e.g. digital angle transducers or sensors based on the eddy current effect.
For sensors in the motor car area, possibilities for the diagnosis of possible faults are desirable. For resolvers as are the subject matter of the present application, a possible fault to be diagnosed is an open line to the resolver coil for the sinusoidal or cosinusoidal signal, i.e. in the case of at least one of the two coils, one of its two terminals no longer has an electrical connection to the drive circuit or there is a cable fracture within one of the two coils.
One possibility of diagnosing such a fault consists in that one of the two signal lines is drawn into the clipping range by a corresponding hardware circuit, i.e. the voltage at the ends of the potentially interrupted signal line is drawn into the overdrive range of the associated AD converter. Such a diagnosis is not sufficiently reliable, however, because clipping can also occur for other reasons.